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Subject[PATCH RFC tip/core/rcu 25/28] rcu: Deconfuse dynticks entry-exit tracing
Date
From: Paul E. McKenney <paul.mckenney@linaro.org>

The trace_rcu_dyntick() trace event did not print both the old and
the new value of the nesting level, and furthermore printed only
the low-order 32 bits of it. This could result in some confusion
when interpreting trace-event dumps, so this commit prints both
the old and the new value, prints the full 64 bits, and also selects
the process-entry/exit increment to print nicely in hexadecimal.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
include/trace/events/rcu.h | 15 +++++++++------
kernel/rcu.h | 7 +++++++
kernel/rcutiny.c | 28 +++++++++++++++++-----------
kernel/rcutree.c | 35 ++++++++++++++++++++---------------
4 files changed, 53 insertions(+), 32 deletions(-)

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 172620a..c29fb2f 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -246,21 +246,24 @@ TRACE_EVENT(rcu_fqs,
*/
TRACE_EVENT(rcu_dyntick,

- TP_PROTO(char *polarity, int nesting),
+ TP_PROTO(char *polarity, long long oldnesting, long long newnesting),

- TP_ARGS(polarity, nesting),
+ TP_ARGS(polarity, oldnesting, newnesting),

TP_STRUCT__entry(
__field(char *, polarity)
- __field(int, nesting)
+ __field(long long, oldnesting)
+ __field(long long, newnesting)
),

TP_fast_assign(
__entry->polarity = polarity;
- __entry->nesting = nesting;
+ __entry->oldnesting = oldnesting;
+ __entry->newnesting = newnesting;
),

- TP_printk("%s %d", __entry->polarity, __entry->nesting)
+ TP_printk("%s %llx %llx", __entry->polarity,
+ __entry->oldnesting, __entry->newnesting)
);

/*
@@ -470,7 +473,7 @@ TRACE_EVENT(rcu_torture_read,
#define trace_rcu_unlock_preempted_task(rcuname, gpnum, pid) do { } while (0)
#define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, grplo, grphi, gp_tasks) do { } while (0)
#define trace_rcu_fqs(rcuname, gpnum, cpu, qsevent) do { } while (0)
-#define trace_rcu_dyntick(polarity, nesting) do { } while (0)
+#define trace_rcu_dyntick(polarity, oldnesting, newnesting) do { } while (0)
#define trace_rcu_callback(rcuname, rhp, qlen) do { } while (0)
#define trace_rcu_kfree_callback(rcuname, rhp, offset, qlen) do { } while (0)
#define trace_rcu_batch_start(rcuname, qlen, blimit) do { } while (0)
diff --git a/kernel/rcu.h b/kernel/rcu.h
index f600868..aa88baa 100644
--- a/kernel/rcu.h
+++ b/kernel/rcu.h
@@ -30,6 +30,13 @@
#endif /* #else #ifdef CONFIG_RCU_TRACE */

/*
+ * Process-level increment to ->dynticks_nesting field. This allows for
+ * architectures that use half-interrupts and half-exceptions from
+ * process context.
+ */
+#define DYNTICK_TASK_NESTING (LLONG_MAX / 2 - 1)
+
+/*
* debug_rcu_head_queue()/debug_rcu_head_unqueue() are used internally
* by call_rcu() and rcu callback execution, and are therefore not part of the
* RCU API. Leaving in rcupdate.h because they are used by all RCU flavors.
diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
index 089820d..e0df33f 100644
--- a/kernel/rcutiny.c
+++ b/kernel/rcutiny.c
@@ -54,20 +54,21 @@ static void __call_rcu(struct rcu_head *head,

#include "rcutiny_plugin.h"

-static long long rcu_dynticks_nesting = LLONG_MAX / 2;
+static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;

/* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
-static void rcu_idle_enter_common(void)
+static void rcu_idle_enter_common(long long oldval)
{
if (rcu_dynticks_nesting) {
- RCU_TRACE(trace_rcu_dyntick("--=", rcu_dynticks_nesting));
+ RCU_TRACE(trace_rcu_dyntick("--=",
+ oldval, rcu_dynticks_nesting));
return;
}
- RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting));
+ RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
if (!idle_cpu(smp_processor_id())) {
WARN_ON_ONCE(1); /* must be idle task! */
RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
- rcu_dynticks_nesting));
+ oldval, rcu_dynticks_nesting));
ftrace_dump(DUMP_ALL);
}
rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
@@ -80,10 +81,12 @@ static void rcu_idle_enter_common(void)
void rcu_idle_enter(void)
{
unsigned long flags;
+ long long oldval;

local_irq_save(flags);
+ oldval = rcu_dynticks_nesting;
rcu_dynticks_nesting = 0;
- rcu_idle_enter_common();
+ rcu_idle_enter_common(oldval);
local_irq_restore(flags);
}

@@ -93,11 +96,13 @@ void rcu_idle_enter(void)
void rcu_irq_exit(void)
{
unsigned long flags;
+ long long oldval;

local_irq_save(flags);
+ oldval = rcu_dynticks_nesting;
rcu_dynticks_nesting--;
WARN_ON_ONCE(rcu_dynticks_nesting < 0);
- rcu_idle_enter_common();
+ rcu_idle_enter_common(oldval);
local_irq_restore(flags);
}

@@ -105,14 +110,15 @@ void rcu_irq_exit(void)
static void rcu_idle_exit_common(long long oldval)
{
if (oldval) {
- RCU_TRACE(trace_rcu_dyntick("++=", rcu_dynticks_nesting));
+ RCU_TRACE(trace_rcu_dyntick("++=",
+ oldval, rcu_dynticks_nesting));
return;
}
- RCU_TRACE(trace_rcu_dyntick("End", oldval));
+ RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
if (!idle_cpu(smp_processor_id())) {
WARN_ON_ONCE(1); /* must be idle task! */
RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
- oldval));
+ oldval, rcu_dynticks_nesting));
ftrace_dump(DUMP_ALL);
}
}
@@ -128,7 +134,7 @@ void rcu_idle_exit(void)
local_irq_save(flags);
oldval = rcu_dynticks_nesting;
WARN_ON_ONCE(oldval != 0);
- rcu_dynticks_nesting = LLONG_MAX / 2;
+ rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
rcu_idle_exit_common(oldval);
local_irq_restore(flags);
}
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 28f8f92..cc04876 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -196,7 +196,7 @@ void rcu_note_context_switch(int cpu)
EXPORT_SYMBOL_GPL(rcu_note_context_switch);

DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
- .dynticks_nesting = LLONG_MAX / 2,
+ .dynticks_nesting = DYNTICK_TASK_NESTING,
.dynticks = ATOMIC_INIT(1),
};

@@ -348,17 +348,17 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
* we really have entered idle, and must do the appropriate accounting.
* The caller must have disabled interrupts.
*/
-static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
+static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
{
if (rdtp->dynticks_nesting) {
- trace_rcu_dyntick("--=", rdtp->dynticks_nesting);
+ trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting);
return;
}
- trace_rcu_dyntick("Start", rdtp->dynticks_nesting);
+ trace_rcu_dyntick("Start", oldval, rdtp->dynticks_nesting);
if (!idle_cpu(smp_processor_id())) {
WARN_ON_ONCE(1); /* must be idle task! */
trace_rcu_dyntick("Error on entry: not idle task",
- rdtp->dynticks_nesting);
+ oldval, rdtp->dynticks_nesting);
ftrace_dump(DUMP_ALL);
}
/* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
@@ -383,12 +383,14 @@ static void rcu_idle_enter_common(struct rcu_dynticks *rdtp)
void rcu_idle_enter(void)
{
unsigned long flags;
+ long long oldval;
struct rcu_dynticks *rdtp;

local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
+ oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting = 0;
- rcu_idle_enter_common(rdtp);
+ rcu_idle_enter_common(rdtp, oldval);
local_irq_restore(flags);
}

@@ -411,13 +413,15 @@ void rcu_idle_enter(void)
void rcu_irq_exit(void)
{
unsigned long flags;
+ long long oldval;
struct rcu_dynticks *rdtp;

local_irq_save(flags);
rdtp = &__get_cpu_var(rcu_dynticks);
+ oldval = rdtp->dynticks_nesting;
rdtp->dynticks_nesting--;
WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
- rcu_idle_enter_common(rdtp);
+ rcu_idle_enter_common(rdtp, oldval);
local_irq_restore(flags);
}

@@ -431,7 +435,7 @@ void rcu_irq_exit(void)
static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
{
if (oldval) {
- trace_rcu_dyntick("++=", rdtp->dynticks_nesting);
+ trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting);
return;
}
smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
@@ -439,10 +443,11 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
/* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
smp_mb__after_atomic_inc(); /* See above. */
WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
- trace_rcu_dyntick("End", oldval);
+ trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting);
if (!idle_cpu(smp_processor_id())) {
WARN_ON_ONCE(1); /* must be idle task! */
- trace_rcu_dyntick("Error on exit: not idle task", oldval);
+ trace_rcu_dyntick("Error on exit: not idle task",
+ oldval, rdtp->dynticks_nesting);
ftrace_dump(DUMP_ALL);
}
}
@@ -453,8 +458,8 @@ static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
* Exit idle mode, in other words, -enter- the mode in which RCU
* read-side critical sections can occur.
*
- * We crowbar the ->dynticks_nesting field to LLONG_MAX/2 to allow for
- * the possibility of usermode upcalls messing up our count
+ * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NESTING to
+ * allow for the possibility of usermode upcalls messing up our count
* of interrupt nesting level during the busy period that is just
* now starting.
*/
@@ -468,7 +473,7 @@ void rcu_idle_exit(void)
rdtp = &__get_cpu_var(rcu_dynticks);
oldval = rdtp->dynticks_nesting;
WARN_ON_ONCE(oldval != 0);
- rdtp->dynticks_nesting = LLONG_MAX / 2;
+ rdtp->dynticks_nesting = DYNTICK_TASK_NESTING;
rcu_idle_exit_common(rdtp, oldval);
local_irq_restore(flags);
}
@@ -2012,7 +2017,7 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
rdp->nxttail[i] = &rdp->nxtlist;
rdp->qlen = 0;
rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
- WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != LLONG_MAX / 2);
+ WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);
WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
rdp->cpu = cpu;
rdp->rsp = rsp;
@@ -2040,7 +2045,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
rdp->qlen_last_fqs_check = 0;
rdp->n_force_qs_snap = rsp->n_force_qs;
rdp->blimit = blimit;
- WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != LLONG_MAX / 2);
+ WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_NESTING);
WARN_ON_ONCE((atomic_read(&rdp->dynticks->dynticks) & 0x1) != 1);
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */

--
1.7.3.2


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